Question

我的asynctask不起作用。该对话框不会被忽略而且列表没有被更新（我认为因为onPostExecute没有被调用）。我用谷歌搜索它，但没有结果。

package com.example.whs;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

import org.apache.http.NameValuePair;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class Albums extends ListActivity {
    // Progress Dialog
    private ProgressDialog pDialog;

    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();

    // Array for the list
    ArrayList<HashMap<String, String>> itemList;

    // url to get the items
    private static String url_all_products = "<my url here>";

    // JSON variables
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_MESSAGE = "message";
    private static final String TAG_ITEMS = "items";
    private static final String TAG_NAME = "name";
    private static final String TAG_ID = "id";
    private static final String TAG_USERNAME = "username";

    //JSON array
    JSONArray items = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_albums);

        // HashMap for the items
        itemList = new ArrayList<HashMap<String, String>>();

        // Loading the items on the background
        new LoadAllItems().execute();

        // Get list-view
        ListView lv = getListView();

        // On item click
        lv.setOnItemClickListener(new OnItemClickListener(){
            public void onItemClick(AdapterView<?> parent, View view, int position, long id){
                //do
            }
        });
    }

    // class for loading all items
    class LoadAllItems extends AsyncTask<String, String, String> {
        // Before 
        @Override
        protected void onPreExecute(){
            super.onPreExecute();
            pDialog = new ProgressDialog(Albums.this);
            pDialog.setMessage("Albums laden...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        // Get the products     
        @Override
        protected String doInBackground(String... params) {
            // Build Parameters
            List<NameValuePair> params1 = new ArrayList<NameValuePair>();
            //Get the JSON string
            JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params1);

            // Check for response
            Log.d("All Items: ", json.toString());

            try {
                // check for success tag
                int success = json.getInt(TAG_SUCCESS);

                if(success == 1) {
                    // found the items
                    items = json.getJSONArray(TAG_ITEMS);

                    // loop through the items
                    for (int i = 0; items.length() > i; i++){
                        // Get the item in variable c
                        JSONObject c = items.getJSONObject(i);

                        // Store in a variable
                        String id = c.getString(TAG_ID);
                        String name = c.getString(TAG_NAME);
                        String username = c.getString(TAG_USERNAME);
                        if(username == ""){
                            username = "onbekend";
                        }

                        // Create the HashMap
                        HashMap<String, String> map = new HashMap<String, String>();

                        // add it
                        map.put(TAG_ID, id);
                        map.put(TAG_USERNAME, username);
                        map.put(TAG_NAME, name);

                        // to arraylist
                        itemList.add(map);
                    }
                }else{
                    // nothing found
                    Intent i = new Intent(getApplicationContext(), Index.class);
                    // close the previous activities                    
                    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(i);
                }
            } catch (JSONException e){
                e.printStackTrace();
            }
            return null;
        }       
    }

    protected void onPostExecute(String result){
        // dismiss dialog
        pDialog.dismiss();      
        runOnUiThread(new Runnable(){
            public void run(){
                // Add adapter to the list
                MenuAdapter adapter = new MenuAdapter(Albums.this, itemList);
                ListView list = (ListView)findViewById(R.id.list);
                list.setAdapter(adapter);   
                }
            });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.albums, menu);
        return true;
    }

}

循环正常工作。

如何解决这个问题？

Answer 1

1）您正在尝试在后台线程中启动活动，请勿执行此操作。

2）你可能会得到一个json异常，只需记录更多内容，这样你就可以看到发生了什么

这些可能就是为什么它永远不会到达onPostExecute

Answer 2

您无法在doInBackGround（）中执行与UI相关的操作，就像您在doInBackground中开始新活动一样，

 Intent i = new Intent(getApplicationContext(), Index.class);
                    // close the previous activities                    
                    i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    startActivity(i);

我的aSyncTask不起作用

2 个答案: